Chemical emissions from the manufacturing processes used in the semiconductor industry represent serious occupational and environmental hazards and as such are closely regulated.
The use and associated emissions of perfluorocompounds (PFCs) as suspected greenhouse gases within the semiconductor industry have indeed received increased attention in recent years. The 1997 Kyoto Protocol provided the impetus for major industries to address global warming issues, and the semiconductor industry has taken a proactive response toward PFC emissions reduction. The World Semiconductor Council (WSC), comprised of the European Electronic Component Manufacturer's Association (EECA), the Electronics Industry Association of Japan (EIAJ), the Korean Semiconductor Industry Association (KSIA) and the Semiconductor Industry Association (SIA) agreed in 1999 to reduce the aggregate absolute emissions of PFCs from semiconductor fabrication facilities to greater than 10% from the baseline year by the year 2010 (the baseline year for EECA, EIAJ, and SIA was set at 1995, and KSIA's at 1997). These goals address greenhouse gas emissions without affecting competitiveness, and allow for a uniform set of guidelines for suppliers and researchers world-wide. Similar PFC reduction initiatives have also been included in the SIA "International Technology Roadmap for Semiconductors" and relationships have been formed between federal regulatory agencies and industry, such as the 1995 memoranda of understanding (MOU) between the EPA and the US semiconductor industry. To attain such goals, it is estimated that PFC emission reductions of 90% for wafer etch and 95% for plasma enhanced chemical vapor deposition (PECVD) chamber cleans compared to 1995 levels will be required for existing 200 mm wafer fabs.
Given the industry's reliance on PFC usage in wafer fabrication, the Roadmap's challenge is compelling. To achieve such a goal requires an aggressive approach involving process optimization, alternative chemistries, PFC recapture/recycle and/or abatement. Beyond the development and implementation of innovative solutions, which are already well underway, accurate characterization techniques are also needed to assess the effectiveness of these solutions. Decisions can then be made based on empirical results, leading to direct reductions in PFC emissions and proper handling of any subsequent chemical by-products.
Because PECVD chamber clean processes can account for 60-90% (with dielectric etch processes accounting for 10-30%) of PFC emissions from 200 mm wafer manufacturing fabs, plasma abatement and nitrogen trifluoride (NF.sub.3)-based chamber cleaning approaches have recently been evaluated within the industry. These approaches have proven to be extremely effective in PFC reduction, but introduce an ancillary challenge, namely the characterization and abatement of molecular fluorine (F.sub.2). Concerns include the emission of HF or other regulated toxic compounds into the air, as well as discharge of ionic fluoride transferred from wet scrubbers into the site's wastewater stream, which can potentially exceed a site's fluoride emission permit. Increased fluoride emission from approaches to reduce PFC emissions can challenge these fluoride ion wastewater discharge limits. The degree to which fluorine will require special treatment depends on the ability to accurately measure concentrations emitted from manufacturing processes in real-time.